1. Field of the Invention
The present invention relates to a novel .beta.-fructofuranosidase with a relatively high fructosyl-transferring activity, its preparation and uses.
2. Description of the Prior Art
Fructosyl-transferred saccharides such as xylosylfructoside and lactosucrose, which are produced by the saccharide-transferring reaction using .beta.-fructofuranosidase (EC 3.2.1.26) or fructosyltransferase to act on sucrose and other saccharide(s) as a substrate, have the properties of an anti-cariogenicity and a growth-promoting activity for bifid bacteria. Therefore, these oligosaccharides are attracting much attention from the food and pharmaceutical fields.
Conventionally known .beta.-fructofuranosidases, which form the fructosyl-transferred saccharides, are those derived from microorganisms of the species Arthrobacter sp. K-1 and Bacillus megaterium (IFO 13498).
"Agricultural and Biological Chemistry", Vol.54, No.4, pp.913-919 (1990) reports that the .beta.-fructofuranosidase of Arthrobacter sp. K-1 has an optimum pH of 6.5-6.8. However, it is not suitable because under the pH range the browning reaction of saccharides readily occurs at temperatures used in the industrial-scale enzymatic reactions. Particularly, the tendency is more critical in the fructose-forming reaction, and this may give an overload to the decolorization steps for purifying saccharides in reaction mixtures. As is disclosed in Japanese Patent Laid-Open No.200,386/92, the .beta.-fructofuranosidase of Bacillus megaterium IFO 13498 has an optimum pH of 6.0. Under the pH condition, reaction mixtures may be less colored. However, the optimum temperature is low as 40-45.degree. C. so that a bacterial contamination may occur when the enzymatic reactions are carried out at around the temperatures.